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Chaozhou, nestled in Pingtung County, southern Taiwan (22.55°N, 120.53°E), occupies a geographically significant position within a subtropical coastal plain. The city’s terrain is predominantly flat, gently sloping towards the Taiwan Strait, facilitating drainage and historically supporting agricultural activities. Surrounded by a mosaic of rice paddies, fruit orchards (particularly mangoes and pomelos), and aquaculture ponds, Chaozhou exhibits a distinct urban-rural gradient. The landscape immediately surrounding the city is intensely cultivated, transitioning to more natural coastal wetlands and mangrove forests further west, along the shoreline. Elevation is minimal, rarely exceeding 20 meters above sea level, which contributes to a tendency for pollutants to accumulate, particularly during periods of stagnant air. Chaozhou’s proximity to the Taiwan Strait introduces a maritime influence, moderating temperatures but also potentially carrying pollutants from shipping lanes or distant industrial zones. While not directly adjacent to major industrial belts, the broader Pingtung region supports some light manufacturing and processing industries, and the city itself has a small commercial sector. The prevailing winds generally blow from the northeast during the winter months, and from the southwest during the summer, influencing the dispersal of any locally generated emissions. The relatively small population of 53,338 contributes to a less dense urban environment compared to Taiwan’s major metropolitan areas, but localized agricultural practices and vehicle traffic still impact air quality.

Chaozhou’s subtropical climate dictates a distinct seasonal pattern in air quality. The wet season, spanning roughly May to September, brings frequent rainfall and high humidity, generally leading to improved air quality as precipitation washes away particulate matter. Monsoon winds from the southwest during this period also aid in pollutant dispersal. However, periods of heavy fog, common in late summer and early autumn, can trap pollutants near the ground, creating localized episodes of reduced visibility and potentially elevated concentrations of certain pollutants. The dry season, from October to April, presents a different challenge. Cooler temperatures and weaker winds, particularly during November and December, can lead to temperature inversions – a phenomenon where a layer of warm air sits above cooler air, preventing vertical mixing and trapping pollutants close to the surface. Agricultural burning, a traditional practice for land clearing and crop residue disposal, is most prevalent during this period, significantly contributing to particulate pollution. January and February often experience the most stable atmospheric conditions, increasing the likelihood of stagnant air and localized pollution events. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during these months, limiting outdoor activity during periods of reduced visibility or noticeable odors. Spring (March-April) sees a gradual improvement as winds increase and agricultural burning decreases, offering a more favourable window for outdoor pursuits. The transition months of October and November require careful monitoring due to the potential for both agricultural burning and temperature inversions.